Audiometer apparatus

ABSTRACT

Disclosed is audiometer apparatus including a tone generator portion, attenuator network, accoustical transducer and twodimensional plotting mechanism for automatically recording the subject&#39;&#39;s response to signals received at the transducer. The tone generator includes a plurality of continuous running oscillators whose discrete frequency signals are coupled through pulser circuitry to the attenuator by way of magnetic reed switches actuated by the movement of the plotter. Hearing loss information is plotted with a pair of different color ink pens disposed within a carriage on the plotting mechanism. Switching mechanisms control the movement of the plotter and the carriage in their respective directions, selectively move the pens into and out of contact with recording material, and switch the signals received by the transducer from one earpiece to the other. Random validity mechanism is incorporated with apparatus for periodically or manually inserting an additional intensity change to the generated tones. Pulser circuitry, utilizing a photoresistor, is adapted for periodic interruption of the generated signal, the rise and decay characteristics of the generated signal being controlled by the circuitry.

United States Patent 1 Cannon et al. [4 1 Feb. 27, 1973 [54] AUDIOMETERAPPARATUS [57] ABSTRACT 7 Inventors; Vernon w Cannon, Austin, Tex;Disclosed is audiometer apparatus including a tone Gordon Stowe,Northbmok L generator portion, attenuator network, accousticaltransducer and two-dimensional plotting mechanism Assign: nelfoneElecmmics Corporation for automatically recording the subjects responseto cmcago signals received at the transducer. The tone generator [22]Fil d; D 21, 1970 includes a plurality of continuous running oscillatorswhose discrete fre uency si nals are con led throu h [2]] Appl l00054pulser circuitry to the atteniator by way of magnet ic reed switchesactuated by the movement of the [52] US. Cl. ..179/1 N plotter. Hearingloss information is plotted with a pair [51] Int. Cl. ..H04r 29/00 ofdifferent color ink pens disposed within a carriage [58] Field of Search..179/l N, 1 MN, 1 AA on the plotting mechanism. Switching mechanismscontrol the movement of the plotter and the carriage References Cited intheir respective directions, selectively move the pens into and out ofcontact with recording material,

UNITED STATES PATENTS and switch the signals received by the transducerfrom 2,563,384 8/1951 Von Bekesy ..179/1 N one earpiece to the other.Random validity 2,985,7l8 5/1961 Hunsicker e N mechanism is incorporatedwith apparatus for periodi- 2,744,l58 5/1956 Grandjot ..l79/l N Cally ormanuany inserting an i i l i t i Primary ExaminerRalph D. BlakesleeAssistant Examiner-Jon Bradford Leaheey AttorneySheldon W. Wilcoff 20w20Ic I 2OI o I AUTO STANT change to the generated tones. Pulsercircuitry, utilizing a photoresistor, is adapted for periodicinterruption of the generated signal, the rise and decay characteristicsof the generated signal being controlled by the circuitry.

15 Claims, 11 Drawing Figures 209 ZIO PATENTEDFEBZYISB 3,718,763

SHEET 10F 7 INVENTORS VERNON W. CANNON GORDON N. STOWE FIG. 4

PATENTED FEB27I373 SHEET 2 BF 7 mm 9N 24mm moss nmN mN INVENTORS VERNONw. CANNON GORDON N. STOWE ATTORNEY NI 009 I NI OOON NI ooom Y NI ooovEON ON EON PATENTEDFEBZYIQH $718,763

sum 3 or 7 INVENTORS VERNON w. CANNON GORDON N. STOWE ATTORNEY PATENTED3,718,763

SHEET t Of 7 F' IG 6 m w o m N TT 8 l 0B x w o o y no 0 o (\1 9 Q 9 co(0 0 w (\l co co N 2s CO m N 2 w "no rn w s -m w o m o w 59 co 9. g o iO *2 r w Q INVENTORS VERNON W. CANNON GORDON N. STOWE ATTORNEY Thisinvention relates generally to audiometers, more particularly toimprovements in automatic audiometers, and even more particularly toimprovements in the tone generation, tone intensity, frequencyselection, and plotter portions of audiometers.

Audiometers have been used for many years as a basic tool for thetesting of hearing and, as such, have been employed by industry,schools, the military, and others, to provide initial screening ofindividual hearing sensitivity, as well as by the medical profession todetect the presence of hearing defects and diseases in humans.

Basically these audiometers comprise a tone generator portion forfurnishing audio signals of discrete frequencies to a set of earphonesworn by the subject being tested, an intensity varying or attenuatorportion for varying the intensity level of the generated tone, and sometype of means for recording the hearing sensitivity of the individualbeing tested in response to the varying frequency and intensity tonesbeing presented thereto.

The increased use of and reliance upon the audiometer have also demandedthat equipment be developed which, among other things, is substantiallyautomatic or self-recording to reduce dependency upon operatortechnicianaccuracy; provide a permanent and accurate record of the hearing statusof both ears of the subject being tested; and afford minimum maintenanceand ease of servicing. In addition, it has been found that it isimportant that some means be incorporated into the audiometer which candetect the malinger or one who is intentionally attempting to alterthetrue test results. To meet these objectives, many forms and designsof audiometers have been developed in the past, all of which have manydisadvantages associated therewith.

It is therefore a primary object of the invention to provide a new andimproved audiometer whose operation and construction overcomes previousdeficiencies and offers advantages heretofore unobtainable.

Itis a further object of the invention to provide im- Another object ofthe invention is the provision of a random validity test which isprogrammed into the operational sequences of the audiometer to insurethe accuracy and reliability of the test results.

In accordance with these and other objects, the

present invention is directed to audiometer apparatusv which not onlyembodies an overall improved and unique construction and operation, butincorporates subsystems which are novel and unique in themselves, andoffers particular adaptability to audiometer apparatus of the typedescribed.

Accordingly, the apparatus includes a tone generator portion which, inits preferred embodiment, comprises a bank of continuously runningoscillators for respectively producing a plurality of output signals ofdifferent frequencies, the output signals therefrom being selectivelyswitched by a unique switching system through an attenuator network toan output audio portion coupled to a set of earphones. Improvedtwodimensional plotting apparatus is provided for recording information,and in particular information representative of the variable intensityand frequency proved audiometer apparatus which is automatic or selfrecording, provides a permanent, continuous, and accurate record of thehearing sensitivity of the subject being tested, and offers increasedreliability in the test results obtained therefrom.

It is a still further object of the invention to provide a new andunique means for the selective switching of the different frequencyaudio signals to the earphones worn by the test subject.

It is an even still further object of the invention to provide a new andimproved non-mechanical signal interrupter or pulser, which interruptercan be advantageously employed in an audiometer to reduce the eardrumfatigue normally associated with a continuous tone as well as toeliminate key clicks normally associated with the switching from onefrequency to the other.

Another object of the invention is to provide improvements in twodimensional plotting apparatus, which improvements may be advantageouslyincorporated into the plotting mechanism of an audiometer forautomatically recording the hearing status of the subject being tested.

signals received by the earphones. The plotting apparatus includescarriage means supporting a pair of writing implements for recording thehearing sensitivity of the subject being tested, the movement of theplotting apparatus, carriage means, and the writing implements beinguniquely controlled by mechanisms and circuitry subsequently described.Means are also provided for the selective coupling of the generatedsignals to either one or the other earpiece of the set of earphones.

Signal interrupting apparatus of unique construction is advantageouslyincorporated between the tone generator portion and the intensityvarying or attenuator portion for selective interruption of the signalsbeing received at the output audio portion. Additionally, a randomvalidity mechanism is incorporated with the audiometer apparatus forperiodically or manually inserting an additional intensity change of thegenerated tones, this insertion, in the preferred embodiment, beingperiodically effected by magnetically operated switching means whichcouples additional resistance with the attenuator network of theapparatus.

Additional features of the invention, as well as further objects andadvantages thereof, will become apparent with reference to the followingdetailed description taken in conjunction with the drawings, in which:

FIG. 1 illustrates a perspective view of the external housing of theaudiometer of the present invention;

FIG. 2 is an overall block diagram schematic of the preferred embodimentof the invention;

FIG. 3 is a partial sectional view of the audiometer taken along thesection line 3-3 of FIG. 1, illustrating the improved plotting mechanismof the invention;

FIG. 4 is a partial sectional view of the plotting mechanism taken alongsection line 44 .of FIG. 3, illustrating additional details of theplotting mechanism;

FIG. 5 is a plan view of a portion of the plotting mechanismillustrating the pen carriage;

FIG. 6 is an exploded perspective view of the pen carriage assembly ofthe plotting mechanism;

FIG. 6a is an enlarged plan view of the pen carriage;

FIG. 7 is a view, partially in section, showing the, motor drive for theoverall plotting mechanism, taken along the line 7-7 of FIG. 3.

FIG. 8 is a schematic of the improved tone or signal interrupter of thepresent invention;

FIG. 9 is a view, partially schematic, of the improved switchingmechanism of the audiometer of the present invention; and

FIG. 10 is an illustration of a typical record of the hearing responseof one ear produced by operation of the audiometer of the presentinvention.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in FIG. 1 an audiometer 20 for use in testing hearing andan earphone assembly 22 with ear pieces 25a and 25b electricallyconnected to the audiometer 20 through cable 24. The audiometer 20 has acover 26, a carrying handle 27 and a control panel 28. The unit 20, dueto its size and construction, is lightweight and portable.

During the course of the test, the earphone assembly 22 is placed overthe ears of the test subject, tones of varying frequency and intensitybeing alternately and automatically presented to the right and left earsthrough ear pieces 25a and 25b, as subsequently described. Atwo-dimensional plotter 30 for permanently recording the subjectsresponse to these tones is disposed over a sheet record material 32mounted thereunder, holes 31 provided therein to enable the recordmaterial 32 to be properly indexed with the plotter 30.

Referring now to FIG. 2, the audiometer 20 includes a tone generatorportion 200 comprising a bank of oscillators 201a through 201f forrespectively producing discrete frequency signals or tones as, forexample, 500 Hz, 1,000 Hz, 2,000 I-Iz, 3,000 Hz, 4,000 Hz, and 6,000 Hz.While each of these oscillators may be of a conventional design, as asignificant feature herein, each oscillator is a continuous running unithaving a substantially constant output amplitude.

A unique switching network 202 couples the output signals from aselected one of the oscillators to the input of a tone interrupter orsignal pulser 205 and thereafter to the audio output portion of thesystem. More specifically; the network 202 includes a plurality ofmagnetic reed switches 203a through 203]. Individual coils 204a through204f are respectively associated with each reed, the coils 204 beingconnected between a common positive voltage supply and respectivecontact terminals 190-196. When a selected coil 204 is excited, it iseffective to close its associated reed switch 203 in a manner well knownin the art, the soclosed reed thus coupling the output signal from itsassociated oscillator 201 to the input of pulser 205.

Selective excitation of the coils 204a through 204f is accomplished bythe connection of the terminals 190-196, respectively, to a commonnegative voltage bus bar 186 by way of a sliding contact assembly 170carried by the plotter 30. As a consequence, the individual frequencysignals or tones are sequentially applied to the input of the pulser 205as the plotter 30 proceeds along its path of travel in the horizontal orX direction. For example, in the system illustrated in FIG. 2, as theplotter proceeds from left to right, sequentially coupling the terminals190-196 to the bus bar 186, an initial 1,000 I-Iz practice tone isselectively switched from the output of oscillator 2011; to the pulserinput, followed sequentially by 500 Hz, 1,000 Hz, 2,000 Hz, 3,000 I-Iz,4,000 Hz, and 6,000 Hz tones. It is thus observed that the outputsignals from each of the continuously running units may be switched tothe audio output portion of the network by use of a non-mechanicalindirect switching technique whereby the switch portions 203a-203fthemselves are protected against fusion, environmental corrosion, andother deleterious efiects which could adversely affect the switchingoperation.

- The selected output signals or tones from the network 200 are thusapplied to a tone interrupter or pulser 205. When the network 205 is inthe CON- STANT position or mode, the tone signals inputed thereto passthrough and are uninterrupted or substantially unafi'ected. When thepulser 205 is in the AUTO position, however, the network 205 iseffective to periodically {interrupt the tone. As subsequentlydescribed, temporary disconnection of the output signals from the tonegenerator portion 200 may also be effected utilizing the network 205during the switching from one frequency to another, thereby eliminatingthe key clicks normally associated with this switching. Control of therise and decay of the frequency signals or tones during the pulsing anddisconnect operation is also maintained by circuitry 205, assubsequently described in greater detail.

The pulsed or constant tone, whichever the case may be, is thereaftercoupled from the output of the interrupter 205 through a conventionalamplifier 206 to an attenuator network 207 for varying the intensity ofthe tone being applied thereto. The attenuator is of conventional designknown in the art and may be a ladderresistor arrangement, asillustrated. A sliding contact 208 mechanically coupled to the carriage54 of the plotter 30 varies the location of the application of theoutput signal from amplifier 206 to this attenuator network in responseto the Y-axis movement of the carriage 54, thus varying the intensity orattenuation of the I tone at the output of the network 207. Theattenuated frequency signal is thereafter coupled through relays 209 and210 to either the right or left earpiece 25a or 25b, respectively, assubsequently more fully described.

The plotting of the hearing sensitivity is effected by the X-Y plotter30 in combination with a sheet of record material 32 which is suitablypositioned under the plotter 30. The plotter 30 is moved in the forwarddirection in the X plane by low-speed motor 42 mechanically coupledthereto, and is moved in the rearward direction in the X plane by highspeed motor 43, each motor being selectively engaged as required. Theplotter 30 carries a pen carriage member 54 which is reversibly movablein the vertical or Y plane by a motor 86. The carriage 54 carries twomarking pens 79 and 81, each of which can be selectively engaged withthe record material 32. These pens are desirably of different colors orother distinguishing characteristics (such as different point widths) sothat a record of the response of both ears of a test subject can berecorded and distinguished on a single sheet of record material,

32. This can be accomplished by having the pen "/9 in engagement withthe record material 32 during the testing of the right ear, for example,while the pen 8] is in engagement with the record material during thetesting of the left ear.

During the testing operation, the plotter 30 is initially disposed inthe left-most position with one of the pens,

for example pen 79, in contact with the record material 32 and thesignal being presented to one of the ear pieces, for example 250. Theplotter 30 is then moved to the right at a continuous rate by X motor 42during which time switch mechanism 170 selectively presents variousfrequencies of audio sound to the earphone a.-During this period, thecarriage 54 (and the sliding contact assembly 208) is alternatelytraveling in opposite directions in the vertical or Y plane, thisvertical movement being controlled by reversible motor 86. As aconsequence, a trace of hearing sensitivity is made on the record 32 inresponse to the frequency and intensity changes of the tone beingpresented to the subject.

When the plotter reaches the right-most position, the motor 42 isdisengaged, the motor 43 engaged, the pen 79 is lifted from the paper,and the plotter 30 is moved to the left-most position. When the plotter30 reaches this left-most position, the pen 81 is placed in engagementwith the paper, the motor 43 is disengaged, and the motor 42 is againengaged to drive the plotter 30 in the forward X direction. The variousfrequencies and intensities are again presented this time to the otherear through earphone 25b until the plotter 30 reaches the right-mostposition whereupon the motor 42 is again disengaged, and motor 43 isengaged to return the carriage to the left-most position, the testthereby being completed.

The motors 42 and 43, which are normally running when power is appliedthereto, have electrically actuated means for the respective engagementand disengagement of clutches (59, 61) of these motors (and theconsequent relative movement of the plotter 30 in the X plane), theengagement and disengagement of the respective motor clutches (thus theengagement and disengagement of the motors) are controlled by relay 215electrically connected thereto; the relay 215 when actuated, causes theplotter 30 to be driven in either the forward or reverse direction.Actuation of this relay 215 is, in turn, effected by a number of inputsthereto. Specifically, forward travel of the plotter 30 is initiallyeffected by depression of start switch 218 which, through cooperation oflogic amplifier 218a, actuates relay 219, the relay 219 then actuatingrelay 215 to engage motor 42 and disengage motor 43. When plotter 30reaches the right-most position (the testing of one ear having thus beencompleted, as subsequently described), it engages limit switch 217 whichthen actuates relay 215 to disengage forward motor 42 and engage returnmotor 43, the plotter 30 thus being returned to its starting position.When plotter 30 reaches this left-most position, limit switch 216 isengaged to actuate relay 215 to disengage motor 43 and engage motor 42to again move plotter 30 in the forward direction (during which time thetesting of the other ear is effected) until limit switch 217 is againreached and plotter 30 returned as before. End cycle lockout switch 223which is connected through relay 210 to the power source (not shown) formotors 42 and 43, is effective to assure that the motors 42 and 43remain energized during the test cycle of both ears, and de-energizesthe motors 42 and 43 when the plotter 30 reaches the left-most positionafter the second ear has been tested.

External stop-switch 220, when depressed, actuates relay 215 throughcooperation with logic amplifier 221 to disengage motor 42 and engagemotor 43 to return plotter 30 to the left-most position and engageswitch 223. Limit switch 222 assures that initiation of movement ofplotter 30 in the forward direction occurs only after plotter 30 hasfirst reached the left-most position. As another particular featureherein, a number of audiometers 20 may be coupled together forsimultaneous testing of many subjects. Initiation of the testing cyclesfor all of these apparatus may then be effected by a signal receivedfrom external start means 218b, rather than from depression of switch218.

During the motion of the plotter 30 in the forward X direction, the Yposition of the carriage 54 on the plotter (consequently the intensityof the sound presented to the particular earphone as well as theposition of the marking pen along record 32) is controlled by thereversible Y motor 86 which, in turn, is controlled by relay 212 which,when actuated, is effective to alternately change the direction ofrotation of the motor 86. A switch 211 is depressed or released by thetest subject in response to the apparent presence or absence of sounddetected by his ear, thereby actuating the relay 212 to alternately movethe carriage 54 back and forth, thus making a record of the hearingsensitivity during the movement of the plotter 30 in the forward Xdirection. Another input from relay 215 actuates the relay 212 to returnthe carriage 54 to the 0 db position in response to the rearward orreturn movement of the plotter 30.

Disengagement of motor 86 is effected by way of inputs coupled from aminimum, say 0 db, limit switch 213 and a maximum, say db, limit switch214 so that if the carriage 54 reaches the 0 or 100 db level, switch 213or 214, respectively, is effective to terminate the direction of travelof the motor 86 and carriage 54.

Relay 210 is effective, when actuated, to switch the transmitted audiosignals or tones of varying frequency and intensity to either theearpiece 25a or 25b. Initial actuation of this relay 210 is in responseto a pulse applied from logic amplifier 214 in response to depression ofstart switch 218 (or signal from 21812). The relay 210 is also actuatedto switch the audio signal from one earpiece to the other when plotter30 reaches the forwardmost position to engage limit switch 227.

Relay 209 is effective to energize either pen marker solenoids 1 14 or 116 to selectively engage pen 79 or 81 with record material 32, as wellas to provide additional attenuation to the transmitted tone, inaccordance with a specific feature herein. Accordingly, one input torelay 209 is provided from the output of relay 210 so that whenever thetones are switches to earpieces 25a or 25b, the respective pen solenoid114 or 116 is actuated. A limit switch 226 is also engagable by theplotter 30 when it is disposed at its forward-most position to deactuateboth solenoids 114 and 116 to lift both pens 79 and 81 and prevent theircontact with record material 32 during return of the plotter 30 to itsleftmost position.

As a particular feature of the invention, an additional loss network isprovided within relay network 209, the loss network, when inserted,providing additional attenuation (decreased intensity) of the audiosignal being presented to the test subject. In this respect, magneticreed switch 229, when closed, inserts this network as, for example, byincorporating additional resistance fected by a magnet 251 which isperiodically rotated in communication with the magnetically actuatedreed switch 229 by motor 250. In this manner, when the motor 250 isstarted, a random insertion of additional attenuation to the tone isprovided at a time unknown to the subject being tested. Insertion of theextra attenuating network may also be manually effected by depression ofswitch 228.

Referring now to FIG. 3, a detail of the plotter 30 is shown with thecover removed. The plotter 30 is constructed from a support member 34,which is mounted to move along elongated tracks 36. These tracks 36(FIGS. 3 and are attached to the audiometer, and are positioned withtheir lengths parallel to the X direction of the plotter travel shown bythe arrow in FIG. 1. A plurality of rollers 38 are mounted to rotateabout shafts 40 and are positioned in cut-out portions 39 in thevertical members 44. These rollers 38 contact the upper surface of theelongated track 36 to roll therealong. By mounting the support 34 inthis manner, it is free to move along the tracks 36 in an X directionwhile being supported by rollers 38.

A suitable motor assembly 40a (comprising motors 42 and 43) can beprovided to move the support 34 along the track 36 in the X direction.This assembly is shown in detail in FIG. 7 as having a support 41attached to a horizontal member 46 with the forward X motor 42 and thehigh speed return X motor 43 mounted thereon. These two X motors haveextending lower flanges 45 which are pivotably mounted on the support 41by pins 47 so that the motors can rotate as shown by arrows 49. Each ofthe X motors is provided with an upper flange 51 between which a tensioncoil spring 53 is attached to resiliently urge the motors to rotate in adirection toward each other. The motors eachhave a gear member 55 whichengages an elongated rack 57 which is in turn mounted on the frame ofthe audiometer and extends along its length in the X direction. It canbe seen that by mounting the motors 42 and 43 in the above describedmanner, that the spring 53 resiliently holds each motor in engagementwith the rack 57. The motors 42 and 43 are provided with theelectrically actuated clutches 59 and 61, respectively, which can beactuated as previously described to selectively drive the plotter 30 inthe desired direction by either motor 42 or 43.

' The carriage member 54 is mounted for reciprocating movement in the Ydirection along the guide members 48 as shown by the arrows in FIGS. 2,3, and 5. The carriage is provided with a plurality of rollers 63 whichcontact and support the carriage on the upper surface of the guidemembers 48.

By examining FIG. 6, the details of the construction of the carriagemember 54 can be seen as consisting of two identical plate-like sidemembers 56 arranged in a spaced parallel relationship and having Vshaped grooves 58 on the inside faces. These inside faces of the I platemembers 56 are also provided with two parallel spaced grooves or cut-outportions 60. These two side members 56 are held together at their endsby end pieces 62 and 64 to form a rigid rectangular-shaped carriage.

Two slide members 66 and 68 are each provided with two extending flanges70 on their outer faces. These two flanges 70 are of a size and relativespacing so that they mate with and slide in the grooves 60. The twoslide members 66 and 68 are also each provided with two verticallyextending openings or slots 72 and 74 which are centered in the verticalgrooves 75 and 76, respectively. A first and second U-shaped pen holder78 and 80 respectively, are provided to support the marking pens 79 and81 in mounting openings 83. The pens 79 and 81 have different color inkand are desirably of the capillary feed type known in the art. The penholder 78 has two pins 82 which are inserted through the openings 72 inthe slide members 66 and 68 and then into the V-shaped grooves 58. Correspondingly, the pen holder 80 is provided with its two pins 84 whichare inserted through the respective openings 74 in the slide members 66and 68 and thereafter into the V-shaped grooves 58. The relativedimensions of the pins 82 and 84 and the grooves 58 are such that thepen holders 78 and 80 are free to move in the vertical direction whenthe pins 82 and 84 are engaged in and movable with respect to the groove58. The pen holders 78 and 80 during the vertical movement are adaptedto slide in grooves 75 and 76, respectively.

Y motor 86 (shown in FIGS. 3, 4 and 6) is attached to and carried by theplotter 30. This Y motor is a reversible AC type and has a drive wheelattached to an output shaft 102. The drive shaft 102 passes completelythrough the wheel 100 and into an attenuator housing 104 in which theattenuator portion 207 is disposed, the housing 104 being suitablymounted on the plotter 30. As can be seen in FIG. 6, a positioning cord106 has one end attached to end piece 62 at 108 with the other endattached to other end piece 64 at 110. The cord 106 engages a pluralityof positioning pulleys 1 12 and is wrappedaround the drive wheel 1,00.Means are provided (not shown) for preventing slippage of the cord 106on the drive wheel 100, so that as the drive wheel 100 is rotated in theclockwise direction, tension is placed on the positioning cord 106 onthe right hand side, and the carriage member 54 is pulled along theguide rods 48 in the direction of arrow 113. It can also be seen thatwhen the drive wheel 100 is rotated in a counterclockwise direction, thepositioning cord 106 is tensioned on the left hand side, and thecarriage member 54 is moved along the guide rods 48 in the direction ofarrow 115. ltcan thus be seen that the position of the carriage 54 canbe selected by operation of the motor 86.

Turning now to the pen switching mechanism, two solenoids 114 and 116are provided with translatable shafts 118 and 120 extending respectivelytherefrom. Actuation of the two solenoids 114 and 116 will result in theretraction of the shafts118'and 120, respectively. The shafts 118 and120 are pivotally attached to right and left leg members 122 and 124 atpivot points I 126. These two leg members 122 and 124 are pivotallyattached at 128 to a support 130. The support 130 is fixed to thehorizontal member 46 and at right angles thereto (FIG. 4). The two legmembers 122 and 124 are connected by a spanning member 132 so that whenone of the leg members is moved, the movement is transmitted through thespanning member 132 to the other leg member. A right spanning pulley 134and a left spanning pulley 136 are rotatably mounted on the spanningmember 132 and are spaced apart as shown in FIG. 6. It can thus be seenthat the leg members can be moved in either direction about their pivots128 by the actuation of the solenoids 114 and 116 so that actuation ofsolenoid 114 rotates the right leg 122 and left leg 124 in acounterclockwise direction about its pivot points 128, thus moving thespanning member 132 from left to right. By actuation of the solenoid116, the whole assembly is moved in the opposite direction.

A first pin actuation cord 138 has one end attached to side members 66and 68 by means of a rod 140 and passes through an opening 142 in theend piece 62 and from there around pulleys 144 and 145. The cord 138then passes around an idler pulley 146, around the left hand spanningpulley 136, by another idler pulley 147, down the length of the support46, and around pulleys 148 and 149, and is thereafter attached to theend piece 64 at 150.

A second pin actuation cord 152 is attached to the side members 66 and68 by a rod 153. The cord 152 then passes through an opening 154 in theend piece 64, around pulleys 155 and 156, then around idler pulley 158and right hand spanning pulley 134, thereafter around another idlerpulley 160 and pulleys 161 and 162, and is thereafter attached to theend piece 62 at 163.

Right and left hand spring members 165 and 166, respectively, areattached between the support member 130 and the right and left hand legmembers 122 and 124, respectively. These springs maintain the legmembers 122 and 124 in a central position when neither of the solenoids114 and 116 are actuated.

Operation of the pen switching portion of the plotter 30 is as follows.If it is desired to move marking pen 79 into contact with the recordmaterial 32, solenoid 114 is actuated to move the spanning member 132 tothe right, thus tensioning pin actuation cord 152 and moving slidemembers 66 and 68 in the direction of arrow 1 13. This relative movementcauses the pins 82 and 84 to also move in the direction of arrow 113along grooves 58 in side members 56 with the pins 82 thus moving downtoward the apex 117 of the grooves 58, the pins 84 moving toward upperright hand portion 119 of the grooves 58. This movement lowers penholder 78 downward until the pen 79 contacts the record material 32while the pin 81 and holder 80 are correspondingly moved away from therecord material 32.

Conversely, to move marking pin 81 into contact with the recordmaterial, solenoid 116 is actuated, thus tensioning pin actuation cord138 and moving slide members 66 and 68 in the direction of arrow 115,pen holder 78 moving toward upper left hand portion 121, and pen holder80 moving downward toward apex l 17, pen 81 thereby being moved intocontact with the record material 32 in the same manner as described withrespect to pin 79 above.

It should also be noted that the pen switching mechanism is so designedthat when it is desired to switch from a first pen to a second pen, thesecond pen will be moved to begin its marking at the same spot that thefirst pen discontinued its marking. This is accomplished by means of theabove-described unique structure of the pen switching mechanism and byexamining FIG. 6a, the advantages of this structure can be more fullyappreciated.

Initially, it is important to appreciate that pens 79 and 81 arecentrally positioned in the pen holders 78 and 80, respectively. Thesepen holders 78 and and the slide, members 66 and 68 are constructed sodistance (A) measured between one end of the slide members and the pen81 and distance (B) measured between the other end of the slide membersand pen 79 remain constant during the pen switching operation. Byselecting dimension (C) measured between the inside surfaces of the endpieces 62 and 64 to equal distance (A) plus distance (B), each pen ismoved to begin marking at the same spot enabling the pens to be switchedduring the test without affecting the accuracy of the record. It canalso be seen that the pens are mounted in such a manner that they areheld against the record material solely by the gravitational force ofthe weight of each pen and its respective holder.

Referring now to FIG. 8, there is illustrated the unique pulser orinterrupter circuitry 205. Ac cordingly, the selected signal or tonefrom switching network 202 is applied at input terminals A and A to aresistor bridging network 300 comprising fixed resistors R R and R andvariable resistor means 301. In accordance with a specific feature ofthe invention, the variable impedance element 301 is a photoresistorhaving two sections 301a and 301b, the resistance of which is controlledby the incidence of light received from a lamp 303 adjacent thereto. Thephotoresistor 301 and lamp 303 are normally packaged together in a lighttight enclosure so that stray light does not affect the operation of theunit. Maximum impedance of the photoresistor 301 (and therefore maximumattenuation of the incoming signal) occurs when the lightoutput from thelamp 303 is at its minimum, and conversely minimum attenuation of theincoming signal is achieved when the light output is at its maximum.Thus, interruption of the incoming signal from 202 may be controlled byregulating the current input to lamp 303.

This regulation is effected by a conventional freerunning multivibratoror flip-flop network 305 comprising matched cross-coupled transistors Qand Q emitter bias and feedback resistors R, and R and collector loadresistors R and R Frequency of oscillation of the multivibrator isdetermined by resistorcapacitor pairs (R and C and (R and C all aspresently known in the art. Desirably, the conduction times oftransistors Q and Q, are equal, thus providing substantially equalpulsing of the incoming signal from 202. Zener regulation of thecollector voltage and filtering is accomplished in conventional mannerby zener diode Z bypass capacitor C and resistor R The lamp 303 isconnected in the collector leg of one of the transistors, for example Qand is excited in response to actuation of, and current flow through,

transistor Q An external switch control 310 coupled to the base oftransistor 0,, determines the state of conduction of transistor 0:, asfollows. When switch 310 is switched to the AUTO position, (thus openingthe con nection to the base of transistor Q the multivibrator willoscillate at its operating frequency, the alternating conduction andnonconduction of the transistor 0;;

thereby causing the lamp 303 to glow or darken, thereby producing apulsed output signal at terminals 8-3. When the switch 310 is.moved tothe CON- STANT position, the positive voltage applied through theexternal resistor 309 is applied to the base of the transistor 0;,thereby being locked into the conduction mode, and the incoming signalfrom 202 passes through the network 205 with a minimum of attenuation.Conversely, when the switch 310 is moved to the OFF position, a negativevoltage from bus bar 186 maintains the transistor 0;, in nonconduction(0., being in conduction), the output from lamp 303 at a minimum and theconsequent high value of resistance presented by resistor 301 providingmaximum attenuation of the incoming signal.

The rise and decay characteristics of the interrupted tone signal frommeans 202 are controlled in the following manner. The attack (or rise)time is controlled by the current supplied to the lamp 303, the lowerthe current, the longer the rise time.

As a significant feature of the circuitry, however, the decay time, aswell as the maximum attenuation of the incoming signal, is controlled bythe portion of the circuitry now described. Transistor Q along with basebias resistors R and R collector and emitter resistors R and Rrespectively, provide a single stage Class A, common emitter amplifierwith emitter degeneration due to R Field effect transistor Q, has itssource and drain terminals coupled to the collector and base oftransistor Q capacitor C providing DC blocking between drain of Q andbase of Q The base of transistor 0 is connected through DC blockingcapacitor C intermediate the two sections of photoresistor 301.

When transistor Q, is driven to saturation (turned on"), maximum shuntnegativefeedback is provided for Q the input impedance Z, of transistor0, thereby being maintained at a minimum. This low input impedance Z,shunts resistor R increasing the overall resistance of network 300, andincreasing the attenuation of the incoming tone signal.

Triggering of the FET Q is effected by the coupling of the gateelectrode thereof to the collector leg of the transistor 0., through thedecay timing network of resistors R and R and capacitor C At the starttime of maximum signal attenuation (Q conducting) capacitor C iscontrolled rate charged through resistor R and transistor 0,. Converselyduring the time of minimum signal attenuation (Q conducting), capacitorC discharges through resistors R R and R In this manner, a controlleddecay time is maintained.

As previously described with reference to FIG. 2, the switchingmechanism 170 is mechanically coupled to plotter 30 so that as theplotter moves in the X direction, discrete frequency tones aresequentially presented to the test subjects ear. As observed in FIGS.3-5, and particularly FIG. 3, the switch mechanism 170 comprises aplurality of switch arms 172, 174, 176, 178 and 180 attached to thevertical member 44 and resiliently held against switch plate 182.

This switching mechanism 170, as well as the switch plate 182, which isattached to the body of the audiometer, is shown in greater detail inFIG. 9. Accordingly, the switch plate 182 has a rectangular shaped faceor substrate 184 formed of electrically nonconductive material uponwhich the contact terminals or pads are disposed. A plurality ofmounting slots 185 through which suitable fasteners (not shown) can beinserted are provided for attachment of the plate 182 to the audiometer.

Disposed along the line 180a are a plurality of conductive terminals198a, 198b, and 198a which are electrically connected by means (notshown) to a positive voltage supply. Disposed along lines 178a and 176aare conductive terminals 190-196 electrically connected by means (notshown) to coils 204a-204f, as illustrated in FIG. 2. Disposed along line172a is bus line contact 186 coupled to negative voltage source (-v).

In addition to the switching arms 172, 174, 176, 178 and 180, mechanismincludes a relay 197 carried thereon which operatively connects theswitching arm 172 (and consequently bus bar 186) to either switching arm17s (and consequently pads 191, 193 or 195 or switching am 176 (andconsequently pads 190, 192, 194 or 196).

The terminal pads 190-196 are so spaced with respect to one another thatadjacent frequency pads (500 Hz and 1,000 Hz, 1,000 Hz and 2,000 Hz,etc.) slightly overlap one another, as illustrated. The edges of thecontact pads 198a, 198b, 1980 are then disposed to be in alignment withthe areas of the overlapping portions. Thus, for example as the switchmechanism 170 moves to the right in conjunction with the plottermovement, the relay 197 is actuated from B to the A position when theswitch arm reaches the left-most edge of the contact 198b, for example,the frequency of the tone to the test subject thus changing from 1,000Hz to 2,000 I-Iz. Switching of the relay 197 back to the B position thenoccurs when the switch arm 180 passes beyond the right end of contactpad 198b, the frequency then becoming 3,000 Hz. The overlapping offrequency pads and 191, 192 and 193, etc. thus avoids discontinuities inthese tones. While the switching arms 172, 174, 176, 178, and 180 areillustrated as being mutually aligned, use of relay 197 avoids thenecessity of direct alignment between arms 176 and 178, and enables theoverlapping of the adjacent frequency pads (190 and 191, 192 and 193,etc.).

As an additional feature, discrete contact pads 188 are provided along aline 174a and have a portion of their areas in mutual alignment with theoverlapping areas of adjacent frequency pads 191 and 192, for example.Each of the pads 188 is electrically connected by means (not shown) tothe base of transistor Q, of pulser 205 illustrated in FIG. 8.Electrical connection of these pads by switch arm 174 to negative busline 186 thus corresponds to to the OFF position of the switch 310illustrated in FIG. 8. In this manner, the

tone may be temporarily interrupted during the transition from onefrequency to the next to eliminate the clicks" normally associated withthis transition.

To conduct a test with the audiometer, earphone set 22 is placed overthe ears of the test subject and the plotter 30 is moved to theleft-most position. The audiometer is then turned on and a 1,000 cycleper second practice audio signal is presented to only the rightearpiece, for example, of the earphone set 22. During this initialperiod, the X motors 42 and 43 remain disengaged so that the plotterremains in the leftmost position, but the Y motor 86 is in the oncondition, its direction of rotation being controlled by the hand switch211, the test subject thus becoming accustomed to the operation of theequipment.

Once a sufficient period of time has passed for the test subject tobecome accustomed to the operation of the audiometer, the X motor 42 isengaged and the plotter is moved slowly to the right with pen 79engaging the record material 32. As the plotter moves from left toright, the switching mechanism 170 selectively presents the initial1,000 cycle test signal to the ear of the test subject and thereafterthe 500, 1,000, 2,000, 3,000, 4,000 and 6,000 cycles per second audiosignals. The record material 32 is aligned under the plotter such thatthe transition between the presentation of audio signals of differentfrequencies correspond to vertical lines 230, 231, 232, 233 and 234 onthe record material 32, as shown in FIG. 10.

As previously described, the vertical position of the carriage 54 iscontrolled by the hand switch 211 which also, in turn, controls theintensity of the sound presented to the ear of the test subject. Duringthe course of the test, the test subject regulates the switch 211 tocontrol the intensity of the sound presented to his ear at his thresholdof hearing. Since the carriage 54 carries the marking pen 79, a record235 of the vertical position of the carriage 54 is made on the recordmaterial 32, an example of which is shown in FIG. 10.

When the carriage 30 has completely moved across the record material tothe end of the last test frequency, pen 79 is lifted from the recordmaterial 32 and the audio signal is removed from the right earpiece.Also, when the plotter 30 reaches the right-most position, the motor 42is disengaged and motor 43 is engaged to return the carriage to theleft-most position whereupon the pen 81 is moved into contact with therecord material 32 and the audio signal is presented to the leftearphone whereupon the plotter 30 moves to the right while the switchmechanism 170 causes the above mentioned frequencies to again beselectively presented to the left earphone. When the plotter 30 againreaches the right-most position, the motor 42 is disengaged and motor 43is engaged to return the carriage to the leftmost position, whereuponthe test is complete. By use of different color ink in pens 79 and 81,both the right and left ear hearing sensitivity may be recorded on thesame chart. FIG. illustrates a typical record of a test of one ear bythe audiometer. Within each frequency increment a large number of peaksand valleys are formed representing the points at which the apparentsound disappeared and reoccurred. The average of these recorded pointsthus represents the threshold of hearing for the test subject at thegiven frequencies.

I The audiometer also has provisions for a random or manual validitytest, as previously described, which may be applied during the course ofthe hearing test either automatically by the audiometer itself or by thetest operator. In this portion of the test, the tone was attenuated anadditional 10 db, for example, the pens being switched on the carriage54 so that the different colored record portion 236 indicated that thevalidity test was in progress. By noting where the pens have changed,(by color change, for example) the operator can determine when thevalidity test was in progress,

and at what frequency this occurred, and by noting the subjects responseto this change in intensity, to verify the authenticity of the test. Thevalidity mechanism itself is arranged to randomly present the 10 dbsignal during the test so that neither the operator nor the test subjectwill know when the validity test will occur. The validity mechanism alsoenables the operator to manually insert the 10 db attenuation, forexample, to the audio signal when he senses that the test subject isattempting to alter the results of the test.

Variations to the disclosed embodiments may be made consistent with theteachings of the present invention. For example, rather than usingdifferent colored ink in the marking pens 79 and 80, other means may beutilized to differentiate therebetween, for example the line widths maybe different.

Additionally, the validity test has been described by reference to theinsertion of additional attenuation to the audio signal presented to thetest subject. Alternatively, it may be desirable to increase, ratherthan decrease, the intensity of the audio signal during the validitytest. Furthermore, it may be desirable, particularly when testingindividuals with high frequency hearing loss, to begin the testing ofeach ear with the intensity level of the tone at a minimum.

Various other alterations or modifications of the disclosed embodiments,as well as other embodiments, may become apparent to one skilled in theart without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:

1. In an audiometer of the type including tone generating means forproducing a plurality of discrete frequency signals, attenuator meansfor varying the intensity of said frequency signals, an audio outputportion for receiving said varying intensity frequency signals, andplotting means for recording information representative of signalsreceived by said audio output portion, the improvement comprising:

a. a plurality of continuous running oscillators providing said tonegenerator means, said oscillators producing output signals havingrespectively separate and distinct frequencies,

b. switching means coupling said tone generator means to said audiooutput portion, said switching means comprising a plurality of firstmeans respectively directly connected to said oscillators, select onesof said plurality of first means, when actuated, coupling the outputsignals from the respectively connected oscillator to the attenuatormeans; said switching means also comprising a plurality of second means,select ones of said second means, when excited, actuating the saidselect ones of said first means, and

c. means carried by said plotting means for actuating the select ones ofsaid second means.

2. The improvement as described in claim 1 wherein said plurality offirst means are normally open magnetic reed switches, said plurality ofsecond means are coils in proximity with said plurality of first means,and the means carried by said plotter is effective to selectively causecurrent to flow through said coils.

3. The improvement as described in claim 2 including an insulatingsubstrate having formed thereon a plurality of electrically isolatedcontact terminals respectively electrically connected to one end of saidplurality of coils and an elongated contact terminal electricallyconnected to a voltage source of one polarity; a second voltage sourceof relatively opposite polarity electri-' cally connected to the otherend of said plurality of coils; and switching means carried by saidplotter for selectively coupling said electrically isolated contactterminals with said elongated contact terminal.

4. Audiometer apparatus, comprising:

a. a tone generator portion for producing signals of discrete anddiffering frequencies,

b. intensity varying means for altering the intensity of said signals,

c. acoustical transducer means including an earphone having right andleft ear engaging portions for reproducing said varying intensitysignals,

. two-dimensional plotting means for recording information on recordmaterial associated therewith representative of said varying intensitysignals reproduced by said acoustical transducer as a function of thedifferent frequencies thereof, said plotting means carrying firstswitching means for selectively coupling select frequency signals fromsaid tone generator to said acoustical transducer means as said plottingmeans moves in one dimension with respect to said record material,

e. carriage means carried by said plotting means movable in the otherdimension with respect to said record material, said carriage meanscoupled to said intensity varying means so that as said carriage meansmoves in said other dimension, the intensity of the signal reproduced bysaid acoustical transducer means is varied, said carriage means alsosupporting a pair of writing implements for marking said recordmaterial, the characteristics of the mark produced by one of saidwriting implements when in contact with said record material differingfrom the characteristics of the mark produced by the other of saidwriting implements,

f. means for first selectively presenting the varying intensity signalsto one of the said ear engaging portions and moving only one of saidwriting implements into contact with said record material during saidfirst selective presentation, and thereafter secondly selectivelypresenting the varying intensity signals to the other of said earengaging portions and moving only the other of said writing implementsinto contact with said record material during the said second selectivepresentation,

. means for selectively controlling the direction of travel of saidplotting means in said one dimension, and

. means for selectively controlling the direction of travel of saidcarriage means in said other dimension.

5. The apparatus as described in claim 4 wherein the said differingcharacteristics of the marks produced by said writing implements iscolor.

6. The apparatus as described in claim 4, wherein said tone generatorportion comprises a plurality of continuously running oscillators, andfurthermore including a bank of magnetically actuated switchesrespectively coupled to the outputs of said continuously runningoscillators, the switching means carried by said plotting meansselectively actuating said magnetically actuated switches.

7. The apparatus as described in claim 6 including an insulatingsubstrate member having a plurality of first conductive terminalsdisposed thereupon respectively coupled to said magnetically actuatedswitches, said plurality of first conductive terminals arranged in apair of vertically disposed rows with the conductive terminals of onerow coupled with the said magnetically actuated switches coupled to theoutputs of the oscillators producing signals having frequencies adjacentthe frequencies of the signals produced by the oscillators coupled tothe magnetically actuated switches coupled to the conductive terminalsof the other row, portions of said conductive terminals of one row beingvertically aligned with portions of said conductive terminals of theother row, a second plurality of conductive terminals disposed upon saidinsulating substrate arranged in a row vertically disposed from saidfirst and second row, portions of said second plurality of conductiveterminals being vertically aligned with the vertically aligned portionsof the conductive terminals of said first and second row, thirdconductive terminal disposed upon said insulating substrate verticallydisposed from the said first and second plurality of conductiveterminals, the said first switching means carried by said plotting meansselectively electrically connecting the first, second, and thirdconductive terminals, thereby to control the selective coupling of thefrequency signals from the said oscillators to said acousticaltransducer means.

8. The audiometer apparatus as described in claim 4 including means forrandomly varying the intensity of said signals and moving one of saidwriting implements out of contact with, and the other writing implementin contact with, the said record material during the time of said randomvariation.

9. The audiometer apparatus as described in claim 8 wherein said firstmentioned intensity varying means is an attenuator, and said randomvarying means is a loss network comprising resistance means which isperiodically coupled with said attenuator to provide additionaattenuation of said signals.

10. The audiometer apparatus as described in claim 4 including signalinterrupting means coupled between said tone generator portion and saidacoustical transducer for controlled interruption of the signalsprovided to said transducer.

11. The apparatus as described in claim 10 wherein said interruptingmeans comprises input and output terminals; variable impedance meanscoupled between said input and output terminals, said variable impedancemeans including a variable impedance photoresistor having two sectionsthereof; a source of light directed to said photoresistor; first meanscoupled to said light source for controlling the intensity of lightimpinging on said photoresistor, thereby to control the impedancepresented to and the interruption of said signals at said inputterminal; second means for controlling the attenuation and the decaytime of the said signals at said input terminal, said means beingcoupled between said first means and an intermediate point between saidtwo sections of said photoresistor, said second means including a firsttransistor having its base coupled to said intermediate point and itsemitter shunting a portion of said variable impedance means; a fieldeffect transistor having its source and drain terminals respectivelycoupled to the collector and base of said first transistor, the gateelectrode of said field effect transistor being connected through aresistorcapacitor timing network to said first means.

12. The apparatus as described in claim 7, including signal interruptingmeans coupled between said tone generator portion and said acousticaltransducer for controlled interruption of the signals provided to saidtransducer, and furthermore including a fourth plurality of conductiveterminals disposed upon said insulatin g substrate in a row verticallydisposed from said first, second, and third plurality of conductiveterminals, each of said fourth plurality being aligned with the alignedportions of the conductive terminals of said first and second row, saidfourth plurality being electrically coupled to said signal interruptingmeans, said first switching means including means for coupling selectones of said fourth plurality to said third conductive terminal, therebyto interrupt signals from said tone generator during the switching ofone frequency signal to another frequency signal to said transducer.

13. An audiometer comprising the combination of tone generating meansfor producing a plurality of discrete frequency signals, attenuatormeans connected to said tone generating means for varying the intensityof said discrete frequency signals, audio output means connected to saidattenuator means for receiving the varying intensity frequency signals,plotting means for recording information representative of the signalsreceived from said audio output means, and means for randomly varyingthe intensity of said frequency signals, said last-named means includingadditional resistance means caused to be periodically coupled to theattenuator means at intervals of time unknown to the audiometer operatoror to the subject being tested.

14. An audiometer as described in claim 13 wherein said means forrandomly varying the intensity of said discrete frequency signalscomprises magnetically operated switch means effective when closed forcoupling said additional resistance means to said attenuator means, andmagnetic means periodically operated for effecting the periodic closingof said switch means.

15. An audiometer as described in claim 14 wherein said additionalresistance means is a loss network which, when coupled to saidattenuator means, increases the attenuation of said discrete frequencysignals.

1. In an audiometer of the type including tone generating means for producing a plurality of discrete frequency signals, attenuator means for varying the intensity of said frequency signals, an audio output portion for receiving said varying intensity frequency signals, and plotting means for recording information representative of signals received by said audio output portion, the improvement comprising: a. a plurality of continuous running oscillators providing said tone generator means, said oscillators producing output signals having respectively separate and distinct frequencies, b. switching means coupling said tone generator means to said audio output portion, said switching means comprising a plurality of first means respectively directly connected to said oscillators, select ones of said plurality of first means, when actuated, coupling the output signals from the respectively connected oscillator to the attenuator means; said switching means also comprising a plurality of second means, select ones of said second means, when excited, actuating the said select ones of said first means, and c. means carried by said plotting means for actuating the select ones of said second means.
 2. The improvement as described in claim 1 wherein said plurality of first means are normally open magnetic reed switches, said plurality of second means are coils in proximity with said plurality of first means, and the means carried by said plotter is effective to selectively cause current to flow through said coils.
 3. The improvement as described in claim 2 including an insulating substrate having formed thereon a plurality of electrically isolated contact terminals respectively electrically connected to one end of said plurality of coils and an elongated contact terminal electrically connected to a voltage source of one polarity; a second voltage source of relatively opposite polarity electrically connected to the other end of said plurality of coils; and switching means carried by said plotter for selectively coupling said electrically isolated contact terminals with said elongated contact terminal.
 4. Audiometer apparatus, comprising: a. a tone generator portion for producing signals of discrete and differing frequencies, b. intensity varying means for altering the intensity of said signals, c. acoustical transducer means including an earphone having right and left ear engaging portions for reproducing said varying intensity signals, d. two-dimensional plotting means for recording information on record material associated therewith representative of said varying intensity signals reproduced by said acoustical transducer as a function of the different frequencies thereof, said plotting means carrying first switching means for selectively coupling select frequency signals from said tone generator to said acoustical transducer means as said plotting means moves in one dimension with respect to said record material, e. carriage means carried by said plotting means movable in the other dimension with respect to said record material, said carriage means coupled to said intensity varying means so that as said carriage means moves in said other dimension, the intensity of the signal reproduced by said acoustical transducer means is varied, said carriage means also supporting a pair of writing implements for marking said record material, the characteristics of the mark produced by one of said writing implements when in contact with said record material differing from the characteristics of the mark produced by the other of said writing implements, f. means for first selectively presenting the varying intensity signals to one of the said ear engaging portions and moving only one of said writing implements into contact with said record material during said first selective presentation, and thereafter secondly selEctively presenting the varying intensity signals to the other of said ear engaging portions and moving only the other of said writing implements into contact with said record material during the said second selective presentation, g. means for selectively controlling the direction of travel of said plotting means in said one dimension, and h. means for selectively controlling the direction of travel of said carriage means in said other dimension.
 5. The apparatus as described in claim 4 wherein the said differing characteristics of the marks produced by said writing implements is color.
 6. The apparatus as described in claim 4, wherein said tone generator portion comprises a plurality of continuously running oscillators, and furthermore including a bank of magnetically actuated switches respectively coupled to the outputs of said continuously running oscillators, the switching means carried by said plotting means selectively actuating said magnetically actuated switches.
 7. The apparatus as described in claim 6 including an insulating substrate member having a plurality of first conductive terminals disposed thereupon respectively coupled to said magnetically actuated switches, said plurality of first conductive terminals arranged in a pair of vertically disposed rows with the conductive terminals of one row coupled with the said magnetically actuated switches coupled to the outputs of the oscillators producing signals having frequencies adjacent the frequencies of the signals produced by the oscillators coupled to the magnetically actuated switches coupled to the conductive terminals of the other row, portions of said conductive terminals of one row being vertically aligned with portions of said conductive terminals of the other row, a second plurality of conductive terminals disposed upon said insulating substrate arranged in a row vertically disposed from said first and second row, portions of said second plurality of conductive terminals being vertically aligned with the vertically aligned portions of the conductive terminals of said first and second row, third conductive terminal disposed upon said insulating substrate vertically disposed from the said first and second plurality of conductive terminals, the said first switching means carried by said plotting means selectively electrically connecting the first, second, and third conductive terminals, thereby to control the selective coupling of the frequency signals from the said oscillators to said acoustical transducer means.
 8. The audiometer apparatus as described in claim 4 including means for randomly varying the intensity of said signals and moving one of said writing implements out of contact with, and the other writing implement in contact with, the said record material during the time of said random variation.
 9. The audiometer apparatus as described in claim 8 wherein said first mentioned intensity varying means is an attenuator, and said random varying means is a loss network comprising resistance means which is periodically coupled with said attenuator to provide additional attenuation of said signals.
 10. The audiometer apparatus as described in claim 4 including signal interrupting means coupled between said tone generator portion and said acoustical transducer for controlled interruption of the signals provided to said transducer.
 11. The apparatus as described in claim 10 wherein said interrupting means comprises input and output terminals; variable impedance means coupled between said input and output terminals, said variable impedance means including a variable impedance photoresistor having two sections thereof; a source of light directed to said photoresistor; first means coupled to said light source for controlling the intensity of light impinging on said photoresistor, thereby to control the impedance presented to and the interruption of said signals at said input terminal; second means for controlling the attenuation and the decay time of the said signals at Said input terminal, said means being coupled between said first means and an intermediate point between said two sections of said photoresistor, said second means including a first transistor having its base coupled to said intermediate point and its emitter shunting a portion of said variable impedance means; a field effect transistor having its source and drain terminals respectively coupled to the collector and base of said first transistor, the gate electrode of said field effect transistor being connected through a resistor-capacitor timing network to said first means.
 12. The apparatus as described in claim 7, including signal interrupting means coupled between said tone generator portion and said acoustical transducer for controlled interruption of the signals provided to said transducer, and furthermore including a fourth plurality of conductive terminals disposed upon said insulating substrate in a row vertically disposed from said first, second, and third plurality of conductive terminals, each of said fourth plurality being aligned with the aligned portions of the conductive terminals of said first and second row, said fourth plurality being electrically coupled to said signal interrupting means, said first switching means including means for coupling select ones of said fourth plurality to said third conductive terminal, thereby to interrupt signals from said tone generator during the switching of one frequency signal to another frequency signal to said transducer.
 13. An audiometer comprising the combination of tone generating means for producing a plurality of discrete frequency signals, attenuator means connected to said tone generating means for varying the intensity of said discrete frequency signals, audio output means connected to said attenuator means for receiving the varying intensity frequency signals, plotting means for recording information representative of the signals received from said audio output means, and means for randomly varying the intensity of said frequency signals, said last-named means including additional resistance means caused to be periodically coupled to the attenuator means at intervals of time unknown to the audiometer operator or to the subject being tested.
 14. An audiometer as described in claim 13 wherein said means for randomly varying the intensity of said discrete frequency signals comprises magnetically operated switch means effective when closed for coupling said additional resistance means to said attenuator means, and magnetic means periodically operated for effecting the periodic closing of said switch means.
 15. An audiometer as described in claim 14 wherein said additional resistance means is a loss network which, when coupled to said attenuator means, increases the attenuation of said discrete frequency signals. 